Abbey Walk is a development of twelve houses built to Level 4 of the Code for Sustainable Homes and also meeting Lifetime Homes standard.
Abbey Walk is the third Greenhomes development, providing improved environmental performance and aiming to design out obsolescence. Full Lifetime Homes standard means flexibility of use in the future and more living space now. Greenhomes have a pitched timber roof and timber floors spanning between cross walls. The lack of internal load-bearing walls will make potential changes easier. This is distinctive of how Greenhomes’ simplicity builds in long life.
The upgrade to Code Level 4 added about 12% to the build cost over an equivalent scheme built to the 2006 Building Regulations. The most significant increases are for windows and solar water heating.
The Brownfield site is in Storrington, West Sussex, close to the South Downs Area of Outstanding Natural Beauty and the newly created South Downs National Park. The main design hurdles were minimising the impact on the existing drainage system and working at the limit of density allowed in the edge of village setting.
The structure sits on piles without any masonry or concrete in the ground. This reduces time, cost, and minimises spoil. A cross-wall construction with clear-span I-beams and web joists provides complete flexibility for the internal layout. The services for the building are entirely accommodated in ducts and voids to permit easy access for upgrading and renewal. This also helps to achieve an airtight construction by avoiding the penetrations in the vapour control layers. Mezzanine platforms exploit space below the warm roof panels that form raking bedroom ceilings.
Airtightness tests in earlier schemes show the timber system achieves around 1.5m3/m2/hr, which is vastly better than the Building Regulations standard of 10 m3/m2/hr. However, considerable training of operatives is needed to achieve this. The thickness of brick saved by using timber-cladding and lime based render gives more room for insulation.
Greenhomes focus on reducing demand before using recycling systems. This, together with short pipe runs, has the knock-on benefit of wasting less energy in hot water. Simple measures include low flush toilets, reduced flow shower heads and taps, and accurate pipe sizing. Rainwater butts are used to collect water for external use. Abbey Walk earns full marks for easing run-off with a sustainable urban drainage system (SUDS). Roof drainage is to soakaways and roads have porous block paving. Flood risk is low.
Greenoak have chosen materials that minimise environmental impact as far as possible. This includes avoidance of PVC and use of steel rainwater goods, clay pipes, non-PVC pipes and wiring, linoleum floor-coverings and organic paints. Sustainable timber and the absence of Portland cement contribute to significant carbon reduction. Careful design, specification and site waste management helps to minimise construction waste. The amount of landfill residents produce is reduced by recycling and composting facilities. Pollution has been reduced by using zero global warming potential of insulants, and the use of formaldehyde-free boards.
Greenoak provides a detailed scheme-specific user guide and contractors follow the Considerate Constructor Scheme. They also monitor energy and water use, air and water pollution. Secured by Design is a basic requirement of Greenoak. Although the site has little ecological value and limited scope for improvement, Greenoak engaged a qualified ecologist to advise on protecting important features. A bat licence was needed for demolition of existing buildings. It was not possible to achieve higher plot ratios due to the rural edge nature of the site.
Awards and Achievements
- Solar hot water system
- 100% low-energy lights
- ‘A’ rated, low NOx emission boiler, with thermal store to run with solar hot water system.
This Code Level 4 design yields CO2 emissions approximately 46% less than a 2006 Building Regulations compliant house. Estimated energy bills will be nearly half than a 2006 Building Regulations compliant house. Greenoak Housing Association's Greenhome model has earned the the Housing Corporation’s Gold Award for environmental sustainability.
Key to U-values: achieved (required under 2006 Building Regulations) W/m2K
Build form: twelve 2, 3 and 4 bed terraced/semi- detached houses, to be built 2008, typical floor area 82m2
Roof: 300 mm of Rockwool insulation in between I beam rafters U-value: 0.15 (0.15)
Floor: suspended timber cassettes on piles with 250mm of Rockwool insulation in between I beam joists, insulating wood fibre board U-value: 0.15 (0.20)
Walls: 205mm Rockwool insulation within cross-battened timber panels, 22 mm Bitroc board, lime render U-value: 0.13 (0.28)
Windows: argon-filled, triple-glazed with low E coating U-value: 0.8 (1.8)
Doors: composite timber U-value: 1.8 (2.1)
Air Permeability: 1.5m3/(h.m2) at 50 Pa
Ventilation: whole house mechanical ventilation with 90% efficient heat recovery
Heating: Sedbuk ‘A’ rated gas boiler linked to thermal store
Renewable energy source: solar thermal flat plate 3m2
Thermal bridging: accredited construction details y-value = 0.06
Target Energy Emission Rate (TER): 22.35
Dwelling Emission Rate (DER): 11.91
Heat Loss Parameter (HLP): 0.81
Standard Assessment Procedure (SAP): 89, Band B
Code for Sustainable Homes (CSH) Level: 4 (provisional)
Links / Contact Details
- Developer: Greenoak Housing Association
- Architect: Jon Broome Architects
- Quantity Surveyor: Dobson White Boulcott
- Energy Strategy: John Willoughby
- Structural Engineer: Ellis & Moore
- M&E Engineer: ndesign
- Ecology: Faber Maunsell
- Constructor: Westridge
Page last updated: 20 August 2010